PSI - Issue 2_B

Stefanie E. Stanzl Tschegg / Procedia Structural Integrity 2 (2016) 003–010 Author name / Structural Integrity Procedia 00 (2016) 000–000

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Conclusions

Most experimental results reported in this study could be obtained by using the time-saving ultrasonic-fatigue testing technique which allows obtaining data at such high numbers (ca. 10 9 to 10 11 ) of cycles that cannot be reached with conventional fatigue testing machines and not only makes VHCF possible but also a better founded statistical validation. Thus, a detailed differentiation of fatigue crack initiation and propagation becomes possible. Main aim of this paper was to show the important role of small non-propagating cracks and the consequences on the fatigue life of two material groups (high-strength material, mainly steels) and a single-phase homogenous ductile material (copper polycrystals). For both groups, surface as well as interior crack initiation could be identified as competing processes. New techniques, especially imaging techniques allowing much higher spatial resolution make a more detailed study of responsible fatigue mechanisms possible nowadays. This opens new perspectives for modeling of these processes and thus performing life-time estimations for constant and variable amplitude loading at manifold accompanying conditions. One of the probably most important features is the possibility of differentiating the growth and arrest properties of already formed small surface and interior small cracks in the VHCF regime. This has been successfully applied to an analysis of different materials in the VHCF regime so that more realistic life time predictions than before became possible which allow, for example, to avoid over-dimensioning machine parts or allow performing more severe load sequences. The results of this study thus in addition demonstrate that experimental studies are indispensable for industrial purposes, whereby the ultrasonic fatigue technique is most useful.

Acknowledgements

The author acknowledges thankfully her co-workers’ experimental assistance at the University of Natural Resources and Life Sciences, BOKU, especially Dr. B. Schönbauer and Dipl.-Ing. M. Meischel.

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